People who ate the most whole grains were at the lowest risk for developing diabetes, according to a recent review of data from the Nurses’ Health Studies and the Health Professionals Follow-Up Study (British Medical J, July 8, 2020;370:m2206). These huge well-known studies involved nearly 200,000 healthy men and women (free of heart disease, diabetes and cancers) for a total of 4,618,796 person-years of follow-up. The review analyzed participants’ total consumption of whole grains and of specific commonly-eaten whole grain foods such as oatmeal, cold breakfast cereals, dark breads, brown rice, added bran or wheat germ, and found that all were significantly associated with a lower risk of type 2 diabetes. Not being overweight reduced diabetes risk even more.

Other studies have shown that eating whole grains helps to prevent or control:
• excess weight (J Nutr, 2012;142:710-6)
• diabetes (PLoS Med, 2007;4:e261)
• heart disease (Nutr Metab Cardiovasc Dis, 2008;18:283-90)
• some types of cancer (J Am Coll Nutr, June 2000; 19(3):300S-307S)
• high blood pressure (Am J Clin Nutr, 2010;92:733-40)

Understanding Carbohydrates
It makes no sense to go on a diet that restricts all carbohydrates because there are good carbohydrates that promote health and there are harmful carbohydrates that cause high rises in blood sugar levels that are associated with increased risk for obesity, diabetes and heart attacks.

Carbohydrates are chains of sugar molecules. They are found in all plants and all foods made from plants. Carbohydrates can be a single sugar, or two, three or more sugars bound together. Thousands of sugars bound together are called starch, and millions of sugars bound together so tightly that they are hard to break down are called fiber or resistant starch. Only single sugars can pass from your intestines into your bloodstream. When you eat, food that contains starch enters your intestines where enzymes knock off each end sugar consecutively and each end sugar is absorbed immediately. All simple sugars and starches that are broken down rapidly go into the bloodstream, which causes blood sugar levels to rise.

Fiber and other resistant starches contain long chains of sugars that cannot release their end sugars, so they are not absorbed in your small intestines and pass on into your colon. Bacteria in your colon ferment some of these carbohydrates and convert them into Short Chain Fatty Acids (SCFAs) that are absorbed into the bloodstream where they lower high blood sugar, insulin, cholesterol, blood pressure and inflammation (Am J Clin Nutr,. 2000;72(6):1461-68). The carbohydrates that are not fermented or eaten by the good bacteria in your colon pass out undigested, adding bulk to your stool and helping to prevent constipation.

Benefits of Eating the Good Carbohydrates
If you are diabetic, pre-diabetic or trying to lose weight, you don’t need to avoid all carbohydrates. You should eat plenty of the carbohydrates that release their sugars slowly and are not absorbed before they reach your colon. You want to restrict carbohydrates that release their sugars rapidly and are absorbed in the upper intestines. The easier it is to break carbohydrates down into single sugars, the higher your blood sugar level rises and the more insulin you produce.

Just 12 weeks on a diet that included whole grain cereals lowered blood sugar, insulin and triglycerides in pre-diabetics (Nutr Metab Cardiovasc Dis, 2014 Aug;24(8):837-44). When blood sugar rises too high, the pancreas releases large amounts of insulin. Since insulin converts extra sugar into triglycerides, high triglycerides are a measure of the harmful effects of high blood sugar levels. Feeding the pre-diabetics refined carbohydrates caused:
• blood sugar levels to rise to increase cell damage,
• blood insulin levels to rise, which increases risk for heart attacks, and
• triglycerides to rise, which makes people fat and worsens diabetes.
When the pre-diabetics ate whole grain cereals, their blood sugar, insulin and triglycerides all went down. For more on pre-diabetes, which is also called metabolic syndrome, see Metabolic Syndrome Predicts Heart Attacks and Diabetes

My Recommendations
The most healthful carbohydrates are those left where nature puts them: in vegetables, fruits, whole grains, beans, nuts and other seeds. The harmful carbohydrates are usually found in processed foods made with refined carbohydrates (flour, white rice, milled corn, potato starch and so forth), and all extracted sugars including fruit juices. If you are trying to lose weight or are diabetic or pre-diabetic, I recommend that you restrict all foods that cause a high rise in blood sugar:
• foods made from flour (such as bakery products, pastas, chips, crackers)
• all drinks with sugar in them (including fruit juices)
• all foods that contain added sugars
Even if you are not trying to lose weight, I recommend limiting these foods to keep from gaining the ten or more pounds that most people add with each passing decade.